In surveying and cartogarphic measuring operations, it is the horizontal distance and the difference in elevation between the measuring instrument and the measurement point which are of basic importance. When making such measurements, the distance between the measuring instrument and the measurement point is the basic measurement, and in recent times this measurement is often made using electronic distance measuring instruments. The horizontal distance and the elevational differences are determined by multiplying the distance between the instrument and the measurement point by the sine and cosine respectively, of the vertical angle defined by the line of sight of the distance measuring instrument in relation to the true horizontal.
Previously, this vertical angle has often been measured with the aid of a theodolite which includes an accurately marked glass scale serving as an indicator. It is also previously known to use theodolites having accelerometers for providing angular information, wherein the earth's gravational forces are used instead of actual acceleration. A disadvantage of using accelerometers in this manner is that firstly, accelerometers of the class required for such a purpose provide a degree of accuracy of approximately 10.sup.cc and thus are extremely expensive and complex devices. Secondly, it is the acceleration which is determined and not primarily the angular position. This means that conversion to the sine or cosine of the angular position is dependent upon the "g"-acceleration at the measuring site.
Accelerometers are usually constructed such that a mass is displaced linearly along an axis. Attempts have been made to as closely simulate this condition as possible, since it is actually the acceleration along the axis in question which is often to be measured. When this is translated to accelerometers for measuring the angular position in the vertical direction, the corresponding measurement is that of the effect exerted by the downwardly directed "g"-acceleration perpendicularly to an angularly located axis from an absolute horizontal position or line.
The highly accurate accelerometers hitherto constructed for use as angle-measuring devices have normally involved a system in which an electromagnetic or electrostatic power source is used to return a mass (a weight) to a given zero-position. Conventionally, the zero-position is sensed electromagnetically, capacitively or optically and an amplifier amplifies the resultant error signal. The current supplied to the power source is such that the force exerted by the mass as a result of the "g"-acceleration is equalized and this current is measured either directly or by measuring the current across a resistance connected in series with the power source. The measured current, or corresponding voltage, thus constitutes a measurement of the acceleration.
Instruments of this kind are generally expensive, in that, inter alia, the components used therein must be extremely accurately produced. In addition, there are demanding requirements with respect to stability and to providing a low degree of friction. It is noted that a resolution requirement of 10.sup.cc (one revolution here is divided into 400.degree.) is equal to EQU g/64 000=1.6.multidot.10.sup.-5 g